1. Field of the Invention
The invention relates generally to hydraulic brake system as used in motor vehicles. More particularly, the present invention relates to a slidable caliper having opposed inboard and outboard hydraulically actuated pistons for forcing a pair of inner and outer brake pads into frictional engagement with a rotatable brake disc.
2. Disclosure Information
Floating or sliding disc brake calipers are well known in the art. A master cylinder generates a hydraulic signal which is communicated to several brake actuators via brake lines. The signal drives a piston disposed within the sliding caliper, which in turn forces an inboard brake pad into frictional engagement with a rotatable brake disc. A reaction force is generated which causes the floating caliper to slide inboard, drawing an outboard brake pad into frictional engagement with the rotatable brake disc. Upon release of the brake signal, the brake pads must retract from the brake disc to prevent frictional driving losses, as well as undue wear on the braking components.
Known floating calipers utilize an elastomeric seal to forcibly retract the piston, which works in combination with general vibration to drive the inboard pad away from the brake disc. The floating caliper must slide away from brake disc to draw the outboard pad away from the brake disc. This is generally accomplished with some form of elastomeric device on the caliper mounting screws, together with vibrations of the assembly. It has been observed that in field use, the retraction efficiency of known floating calipers degrades with time, especially with respect to the outboard pad. Much effort has been directed at improving the sliding of the caliper, but these are generally costly, complex and less than completely satisfactory.
Another solution has been to provide two opposed, hydraulically actuated pistons within the caliper, the second piston being a mirrored copy of the inboard piston assembly located on the outboard side of the brake disc. This has proven to be particular effective at retracting the brake pads, however, due to the increased size of the caliper, it can only be packaged on vehicles having very large wheels. Therefore, this solution has been restricted to a very small percentage of the vehicles on the road having unusually large wheel and tire assemblies.
It would therefore be desirable to provide a disc brake apparatus capable of positively retracting the brake pads for use in vehicles having restricted space for packaging a brake caliper.